Geo <sub> 2 </ Sub>, The Controllable Synthesis Of Beta-ga <sub> 2 </ Sub> The O <sub> 3 </ Sub> Nanostructures And Their Luminescent Properties,

Patterned nanowire arrays and nanowire networks of GeO₂ and microbelts and hexagonal nanodisks of Ga₂O₃ have been synthesized on the surface of silicon wafer and gallium grain on a large scale,respectively.The morphologies,crystal structures and photoluminescence properties of the GeO₂ and Ga₂O₃ nanostructures were investigated,and the possible growth mechanisms were also proposed to account for the formation of GeO₂ and Ga₂O₃ nanostructures with different morphologies.These investigative results would provide a base for research of photoelectric properties and application of GeO₂ and Ga₂O₃ nanostructures.(1) Synthesis and photoluminescence of patterned well-aligned GeO₂ nanowire arrays: Patterned GeO₂ nanowire arrays have been synthesized on the surface of Au coated silicon wafer on a large scale by heating germanium powders from 900 to 1000℃under the atmospheric condition. The GeO₂ nanowire arrays were single crystalline phase with the hexagonal structure.The diameters and the lengths of GeO₂ nanowire arrays were controlled in the range of 60-70 nm and 4-20μm by varying the heating temperature and time,respectively.The growth of GeO₂ nanowire arrays was under the control of the Vapor-Liquid-Solid mechanism.Two strong UV emissions with peaks at 347 and 364 nm and two blue emissions with peaks at 403 and 490 nm were observed in the GeO₂ nanowire arrays.The UV and blue emissions may be assigned to transition between the oxygen vacancy and interstitial oxygen and radiative recombination between an electron on an oxygen vacancy and a hole on an germanium-oxygen vacancy center in the GeO₂ nanowire arrays, respectively.(2) Synthesis and photoluminescence of sheet-like GeO₂ nanowire networks:GeO₂ nanowire networks have been synthesized on the surface of silicon wafer on a large scale by heating the mixture powders of germanium and aluminium at 1000℃under the O₂ flow.The GeO₂ nanowire networks were single crystalline phase with the hexagonal structure.The diameters and the lengths of GeO₂ nanowire networks were easily controlled by varying the heating temperature and time.The growth of GeO₂ nanowire networks was under the control of the self-catalytic Vapor-Liquid-Solid mechanism.A strong UV emission with peaks at 365 nm and two blue emissions with peaks at 401 and 489 nm were observed in the GeO₂ nanowire networks.The UV and blue emissions may be assigned to transition between the oxygen vacancy and interstitial oxygen and radiative recombination between an electron on an oxtygen vacancy and a hole on an germanium-oxygen vacancy center in the GeO₂ nanowire networks,respectively.(3) In situ growth of single crystallineβ-Ga₂O₃ microbelts with strong photoluminescence: Microbelts of Ga₂O₃ have been in-situ grown on the surface of gallium grain by heating metallic gallium under the flow of Ar for 1h with the existence of water.Synthesized products are all single crystalline phase with the monoclinic structure of Ga₂O₃.The Ga₂O₃ microbelts have widths in the range of 10-20μm and the lengths of about 200μm at least.The influences of the reaction temperature and time on the products were experimentally investigated,and a possible mechanism was also proposed to account for the formation of Ga₂O₃ microbelts.The Ga₂O₃ microbelts exhibited a strong blue emission with peak at 469 nm.The blue emission originated from the recombination of an electron on an oxygen vacancy and a hole on a gallium-oxygen vacancy pair.(4) Single-crystallineβ-Ga₂O₃ hexagonal nanodisks:synthesis,growth mechanism and photocatalytic activity:β-Ga₂O₃ hexagonal nanodisks were in situ grown on the surface of gallium grain and Si substrate via a reaction of metallic gallium with NH₄Cl and H₂O at 650-800℃for 30 min.The as-synthesized nanodisks have perfect hexagonal shape with diagonals of 0.6-4.0μm and thicknesses of 140-480 nm.Size of the hexagonal nanodisks increased with increasing the heat treatment temperature.The role of NH₄Cl in the formation of the hexagonal Ga₂O₃ nanodisks was investigated,and a possible mechanism was also proposed to account for the growth of the hexagonal nanodisks.Photoluminescence and photocatalytic activity of the hexagonal Ga₂O₃ nanodisks were studied at room temperature.The results indicated that the hexagonal nanodisks displayed a stable blue-green emission band centered at 489 nm originated from the recombination of an electron on an oxygen vacancy and a hole on a gallium-oxygen vacancy pair and high photocatalytic activity in the photodegradation of methyl orange..